The present invention relates to an inkjet recording apparatus of a serial recording type provided with a recording head that ejects ink toward a recording medium such as recording paper and a conveying device such as a conveyer roller that coveys the recording medium.
In an inkjet recording apparatus of a serial recording type, as is well known, when ink is not ejected from a recording head toward a recording medium, the recording medium is displaced, while when the recording medium is not displaced, the recording head is made to reciprocably scan and eject ink toward the recording medium. Thus, images or characters are recorded on the recording medium. In other words, intermittent conveyance of the recording medium and recording of an image or the like are repeated in turn so that a piece of image or the like is formed in the inkjet recording apparatus.
In such an inkjet recording apparatus, in which a piece of image is formed while the recording medium is intermittently conveyed, the following problem is likely to be caused. Specifically, if the conveying amount differs at each conveyance, and points of ink droplets deposited (landing) on the recording medium are different from intended controlled points, a white line or a thick line (such defective recording is hereinafter referred to as “banding”) extending in a direction parallel with a scanning direction (a main scanning direction) of the recording head is likely to appear, as shown in FIG. 20.
Major causes of banding are, for example, a low stopping accuracy of the conveying roller and eccentricity of the conveying roller. Improvement in the stopping accuracy of the conveying roller or reduction of the eccentricity of the conveying roller requires use of an expensive motor or a component with a high accuracy, and thus is likely to cause an increase in manufacturing cost of the inkjet recording apparatus.
There is a known technique in which banding is prevented from appearing by first determining the number of scannings based on an arrangement pitch kq of recording elements in a recording head and an pixel pitch q of an image and subsequently ejecting ink a plurality of times toward a point in the same position to create an image.
Since a variety of components in actual products have dimensional variations within respective specified ranges, individual products are usually slightly different from one another in stopping accuracy of a conveying roller and in eccentricity of the conveying roller.
Accordingly, if the above technique is applied to actual commercial products, an actual inkjet recording apparatus will be different from an ideal inkjet recording apparatus or an experimental inkjet recording apparatus, which is used for determining a scanning number, due to variations in individual products. It is, therefore, difficult to securely prevent appearance of banding.
It is required to increase dimensional accuracy and the like of each of the components in order to reduce variations in individual products. Then, application of the above technique will lead to an increase in manufacturing cost of the inkjet recording apparatus.